ISSN:0021-2148    

DOI:10.1002/ijch.199300018

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractWe report a study of the UV photolysis of I3−in alcohol solutions, using femtosecond time‐resolved transient transmission experiments. We interpret our results to indicate that photoexcitation leads to direct formation, within 300 fs, of diiodide ions which are vibrating coherently. The time scales for vibrational dephasing, vibrational relaxation, and reorientation of the fragment ions are 400 fs, 4 ps, and 5 ps, respectively. UV transient transmission experiments were conducted in order to characterize the time scales for recombination. Recombination takes place on several time scales. A fast component is assigned to primary recombination, followed by vibrational relaxation on the ground state of I3−. The prominence of this recombination route is found to be strongly dependent on the solvent. Finally, time domain quantum simulation techniques are employed in order to gain insight into the nature of the nascent diiodide vibrational distribution, and to introduce a semiquantitative model for the stage of bond fission for isolated

ISSN:0021-2148    

DOI:10.1002/ijch.199300019

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThis paper describes experimental studies of the friction a solute molecule experiences in a solvent. More specifically, this work focuses on the dielectric friction needed to describe the rotational diffusion of medium‐sized molecules (displaced volume of a few hundred cubic angstroms) in polar solvents and electrolyte solution

ISSN:0021-2148    

DOI:10.1002/ijch.199300020

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe barrierless isomerization of 1,1‐diethyl‐4,4‐cyanine in alcohol solutions has been studied with 75‐fs laser pulses in transient absorption experiments. The measured dynamics are compared with Monte‐Carlo simulations based on the BFO‐theory (Bagchi, B.; Fleming, G.R.; Oxtoby, D.W.J. Chem. Phys.1983.78:7375) for condensed‐phase barrierless isomerizations, and the viscosity dependence of the long‐time exponential decay is well reproduced with a coherent set of parameters. In the most viscous solvents, early‐time (≲ 1 ps) kinetics are observed which are characteristic of damped wavepacket dynamics in the

ISSN:0021-2148    

DOI:10.1002/ijch.199300021

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractA remarkably good correlation between the rate of proton transfer from excited protonated 1‐aminopyrene and the gas phase basicities of the organic component in water: organic solvent binary mixtures has been found. We suggest that use of anilinium acids minimizes the effect of anion solvation and Coulomb interactions and enables the influence of the organic cosolvent on the proton transfer to be clearly observed. The model proposed is one in which the proton is always transferred to a water molecule and a concerted proton transfer to a water molecule solvated by the organic cosolvent also occurs. The cosolvent influence is then on this latter species via hydrogen bond interactions. The correlation holds in pure water but not in pure organic solvents where, clearly, the proton must be transferred to the organic molecul

ISSN:0021-2148    

DOI:10.1002/ijch.199300022

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe proton transfer (PT) process in the excited hydrogen bonding (HB) complex of 1‐pyrenol and triethylamine, leading to the formation of a hydrogen‐bonded ion pair (HBIP*) of excited pyrenolate anion and triethylammonium cation, PyO−*··· H‐N+(C2H5)3, and subsequent reaction processes of HBIP* in various solvents were investigated by picosecond and femtosecond laser photolysis, as well as by steady‐state absorption and fluorescence measurements. Time constants for the PT process taking place in the time region of a few picoseconds were almost independent of the polarity of the solvent and it was suggested that the intermolecular slow motion in the HB complex, such as the intermolecular vibration and/or the torsional motion of the two moieties, might regulate the PT process. Moreover, the ionic dissociation process following the photoinduced PT process in polar solvent was directly measured. The dynamic behaviors of the excited intermolecular HB complex and underlying mechanisms are discussed by comparing these results with those on the intramolecular photoinduced PT process and with results of investigations of electron tran

ISSN:0021-2148    

DOI:10.1002/ijch.199300023

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractElectron transfer between excited donor molecules followed by the back reaction is treated theoretically for a solid solution at high excitation power. An expression for the average donor cation probabilityP+(t)is derived. Calculations of the time dependence forP+(t)are presented. The results indicate that the maximum value ofP+(t)in the nonlinear quenching process is less than the corresponding values ofP+(t)for the linear quenching at a low excitation power due to the depletion of the acceptors with timet.The restriction of the reaction volume slows down the charge separation if the back charge transfer takes place.

ISSN:0021-2148    

DOI:10.1002/ijch.199300024

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe class of compounds containing a carbonyl group substituted at the 9 position of anthracene have been studied as new model systems for torsional isomerization in solution. Franck‐Condon excitation yields an excited‐state distribution near the barrier for isomerization in S1. Using time‐resolved fluorescence spectroscopy, we have determined that the relaxation from the barrier region is subpicosecond for three different compounds in all solvents studied. In fact, the relaxation seems to be almost independent of solvent at room temperature, indicating that most of the local friction felt by the twisting carbonyl is internal friction rather than solvent friction. Apparently the small carbonyl is effectively shielded from the solvent by the anthracene ring so the solvent friction is not strong. In contrast to the weak solvent coupling, previously reported gas‐phase spectra indicate that the torsion may be strongly coupled to the other vibrational modes of the molecule. Energy flow out of the torsion into these other vibrational modes appears to occur on the subpicosecond tim

ISSN:0021-2148    

DOI:10.1002/ijch.199300025

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractCoherent anti‐Stokes Raman scattering (CARS) from the C=C stretching band region of retinal, recorded with low‐power, 7‐ps (fwhm) laser excitation selected to be in electronic resonance with the retinal chromophore, is presented for light‐ and dark‐adapted bacteriorhodopsin (BR) samples. By minimizing photochemistry with low‐power excitation, the picosecond resonance CARS (PR/CARS) spectrum of BR‐570 (13‐trans, 15‐anti‐retinal) is obtained directly from the light‐adapted BR sample. The PR/CARS spectrum of BR‐548 (13‐cis, 15‐synretinal) is derived from a quantitative analysis of PR/CARS data from dark‐adapted BR which contains comparable amounts of BR‐570 and BR‐548. Band origin positions, lineshapes, relative intensities, and phase factors describing the electronic resonances are obtained from a quantitative fit of the PR/CARS spectra to third‐order susceptibility (χ(3)) relationships. These PR/CARS data, the first reported for a molecular system as large as BR, demonstrate the experimental viability of CARS for recording the vibrational spectrum of a chromophore within a trans‐membrane protein. In addition, the χ(3)analysis shows that a CARS spectrum of a mixture of isomeric chromophores can be quantitatively separated into CARS data assignable to its individual components. The significance of these results with respect to analyzing picosecond time‐resolved CARS data from interm

ISSN:0021-2148    

DOI:10.1002/ijch.199300026

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY

摘要:

AbstractThe radiationless relaxation of dicyanineAmolecules inn‐alcohols methanol to butanol has been studied by picosecond fluorescence spectroscopy and time‐resolved nonlinear spectroscopy. The fluorescence decay rates have been measured as a function of viscosity, temperature, and fluorescence wavelength. It is shown that the wavelength dependence can be explained by coexistence of two ground‐state conformers. The intrinsic activation barrier for the nonradiative decay from the excited surface is very small, much less than 1 kcal/mol. In a particular solvent the time constants of the nonradiative relaxation show a linear dependence on the variation of viscosity. The experimental data are discussed in relation to the BFO theory (Bagchi, B.; Fleming, G.R.; Oxtoby, D.W.J. Chem. Phys.1983,78:

ISSN:0021-2148    

DOI:10.1002/ijch.199300027

出版商:WILEY‐VCH Verlag    

年代:1993

数据来源: WILEY